Surveillance of SARS-CoV-2 in Healthcare Workers before and after COVID-19 Vaccination: A Cohort Study in a Primary Care Unit of Brazil

Introduction: Healthcare workers (HCW) are at higher risk of SARS-CoV-2 infection. Viral surveillance for early detection of COVID-19 is a critical strategy to understand the infection dynamics in this population and to prevent transmission. The study examines SARS-CoV-2 infection and reinfection among HCW vaccinated against COVID-19 who are employed at a primary health care unit serving a disenfranchised community of Brazil. Methods: The study was conducted in Cidade Estrutural, Federal District of Brazil, between February and October 2021. Participants were interviewed and provided samples. A prospective open cohort study was used to analyze the frequency of SARS-CoV-2 infection and reinfection. Nasopharyngeal and peripheral blood samples were collected from workers presenting with flu-like symptoms and subjected to RT-qPCR and serological testing (IgM and IgG chemiluminescence). The frequencies of infection and reinfection (RT-qPCR positive results 90 days after the infection) were calculated along with their respective confidence intervals (95%CI). Results: Of the 128 workers, 61 (47.65%; CI: 39.19-56.25) reported probable SARS-CoV-2 infection before vaccination. Of these, 50 (39.06%; CI: 31.04-47.71) had SARS-CoV-2 infection after vaccination, confirmed by molecular tests. Reinfection was identified in seven workers (14.00%; CI: 6.95-26.18), based on the 90-day interval between results. The serological data from the 128 workers during the cohort indicated that 68 had IgG antibodies (53.12%; CI: 44.5-61.5) and 46 had IgM antibodies (35.93%; CI: 28.14-44.54) against SARS-CoV-2. SARS-CoV-2 infection was common in community health workers (CHW, 56%), registered nurses (50%), and licensed practice nurses (33%). Following the COVID-19 vaccination, the percentage of infections among CHW decreased from 47.83% to 4.35%. Conclusion: These results demonstrate that (i) approximately 40% of the workers were infected with SARS-CoV-2 in 2021 and (ii) reinfections confirmed by RT-qPCR occurred in 14% of the HCW after vaccination. The results provide valuable insights into the circulation of SARS-CoV-2 among HCW in a primary care unit serving a minoritized community.